The present invention relates to a controller for adjusting the pressure of high-pressure fuel supplied to an in-cylinder injector of an internal combustion engine.
Japanese Laid-Open Patent Publication No. 7-103048 discloses a conventional controller for an internal combustion engine. The conventional controller controls an internal combustion engine that includes an in-cylinder injector and an air-intake passage injector for each of its cylinders. More specifically, when injecting fuel into a combustion chamber in each cylinder, the controller uses an appropriate one of the above two types of injectors according to the engine driving state of the internal combustion engine, such as the engine load and the engine speed.
When fuel is injected from the in-cylinder injector (in-cylinder injection mode), fuel having a high pressure (required fuel pressure) must be supplied to a high-pressure distribution pipe connected to the in-cylinder injector. In a port injection mode in which fuel is to be injected from an air-intake passage injector to an intake port, fuel having a pressure lower than the required fuel pressure is supplied to the air-intake passage injector. This is because the pressure of the intake port is relatively low and thus the air-intake passage injector does not need to inject fuel at high pressure.
In the in-cylinder injection mode, a high-pressure pump pressurizes fuel to raise the pressure of fuel in the high-pressure distribution pipe to the required fuel pressure. In the port injection mode, the high-pressure pump is stopped. Since the high-pressure pump is driven only when necessary, the fuel efficiency of the internal combustion engine is prevented from being lowered.
However, when the high-pressure pump is stopped in the port injection mode, the fuel pressure in the high-pressure distribution pipe is lowered. Thus, when shifting from the port injection mode to the in-cylinder injection mode, the required fuel pressure may not be immediately obtained. This is because even if the de-actuated high-pressure pump is actuated when the driving mode is shifted, the fuel pressure in the high-pressure distribution pipe cannot be instantaneously raised. In this case, in-cylinder injection is performed in a state in which the fuel pressure in the high-pressure distribution pipe is not high enough. As a result, large pulsations of the fuel pressure occur in the high-pressure distribution pipe. The pulsation causes the fuel injection amount to be unstable and degrades the combustion characteristics of the internal combustion engine.
To solve this problem, the high-pressure pump may be actuated even in the port injection mode whenever the fuel pressure in the high-pressure distribution pipe becomes less than or equal to a set pressure. This constantly keeps the fuel pressure in the high-pressure distribution pipe greater than or equal to a predetermined value.
The controller described above raises the fuel pressure in the high-pressure distribution pipe to the required fuel pressure at all times, including when shifting from the port injection mode to the in-cylinder injection mode. Thus, in-cylinder injection is performed in a stable manner. However, the controller actuates the high-pressure pump whenever the fuel pressure in the high-pressure distribution pipe becomes less than or equal to the set pressure in the port injection mode. This means that the high-pressure pump is actuated to maintain the fuel in the high-pressure distribution pipe at the required fuel pressure regardless of whether the driving state is shifted from the port injection mode to the in-cylinder injection mode. Accordingly, the high-pressure pump may be actuated even when there are no changes in the driving state. This lowers fuel efficiency of the internal combustion engine.